The Ground Systems Development and Operations Program completed testing of new traction roller bearings on crawler-transporter 2 (CT-2), on two of the massive vehicle's truck sections, A and C, in late January. The new roller bearing assemblies that were installed on one side of the crawler are visible in this Jan. 31, 2014 image. CT-2 returned to the Vehicle Assembly Building (VAB) at Kennedy Space Center, where work continues to install new roller bearing assemblies on the B and D truck sections.

These crawlers have been in use for 45 years, starting with the Saturn rockets for the Apollo missions to orbit and the Moon. Then they were retrofitted for the space shuttle. Now, the Crawler-Transported 2 has been upgraded to "to increase the lifted-load capacity from 12 million to 18 million pounds to support the weight of the mobile launcher and future launch vehicles, including the SLS and Orion."

For comparison, here's the latest retrofitted version of the crawler...